Atrial fibrillation is the most common sustained arrhythmia in the United States, affecting over 2 million people. Its prevalence increases with age up to 5 percent in people more than 65 years of age. Atrial fibrillation is perpetuated by reentrant wavelets propagating outside the normal cardiac conduction pathway, resulting in rapid, irregular heart rate and the loss of atrioventricular synchrony. Atrial fibrillation is also important because of the associated fivefold increase in incidence of stroke.
Three patterns of atrial fibrillation exist: paroxysmal (intermittent), persistent (but able to be cardioverted), and permanent (cardioversion-resistent), with the pattern progressing over time in a given patient. Two strategies generally exist for managing patients with atrial fibrillation: rate control and anticoagulation versus attempts to restore and maintain sinus rhythm. Generally, in most patients, initial attempts are undertaken to restore sinus rhythm with electrical or pharmacologic cardioversion. Standard anti-arrhythmic agents include amiodarone, procainamide, or quinidine. However, disadvantages associated with anti-arrhythmic therapy are that (1) the anti-arrhythmic agents are pro-arrhythmic, e.g., causing torsades de pointe, (2) the anti-arrhythmic agents often carry significant side effects, such as lupus-like syndrome and agranulocytosis, and (3) even with two anti-arrhythmic drugs, some patients may be resistant to pharmacological therapy, e.g., patients may continue to have at least one episode of atrial fibrillation every two days or frequent isolated atrial ectopic beats (more than 700 per day).
If medical therapy fails to convert atrial fibrillation, electrical cardioversion, either externally or via an implanted device, can be attempted using 100 to 200 W.cndot.s of energy. Anticoagulation is usually recommended to reduce the incidence of embolization associated with cardioversion. Current recommendations suggest long-term anticoagulation for 3 to 4 weeks before cardioversion and 2 to 4 weeks following cardioversion.
Other treatment options for atrial fibrillation include catheter ablation of the atrioventricular (AV) node with pacemaker implantation, or modification of the AV node without pacemaker implantation. However, thromboembolic risk is unchanged and atrial systole is not restored with these procedures. Several alternatives have also been available to interrupt the reentrant wavelets, including extensive surgical, or recently, catheter-medicated atriotomy. Using the current techniques, the success rate of catheter ablation of other sustained atrial arrhythmias, e.g., atrial flutter and sustained atrial tachycardia, has been over 90%. Catheter ablation therefore represents an important alternative to pharmacologic therapy for treatment of atrial fibrillation and other sustained atrial arrhythmias.
In order to ablate the ectopic foci, electrophysiologic study (EPS) is required to locate the foci responsible for triggering of atrial fibrillation. According to Haissaguerre, et al., The New England Journal of Medicine (1998), vol. 339, No. 10, p. 659-666, incorporated herein by reference in its entirety, three multi-electrode catheters are introduced percutaneously through the femoral veins: one catheter for ablation, one mapping catheter for positioning in the right atrial appendage (for locating ectopic foci in the right atrial and right pulmonary vein) or coronary sinus (for locating ectopic foci in the left pulmonary vein), and another catheter for stimulation of the atrial tissue to induce atrial fibrillation. In this study, patients with paroxysmal atrial fibrillation were found to have ectopic beats originating in the atrial muscle ("atrial foci") and in pulmonary veins (the left superior, left inferior, right superior, and right inferior pulmonary veins). Direct mapping and ablation of the left atrium and pulmonary veins were performed via a transseptal approach through the foramen ovale which lies in the interatrial septum. Alternatively, the catheters may be inserted retrograde in the aorta through the aortic valve and left ventricle. The ablation was performed at the site with earliest recorded ectopic activity.
The ablative techniques used to restore normal sinus rhythm, where the tissue surface is subjected to extreme localized temperature designed to kill cellular structures, can generate necrotic tissue fragments or blood clots. These tissue debris or thrombi may travel downstream from the procedural site to lodge in other organs, causing stroke, myocardial infarction, renal infarcts, and tissue ischemia in other organs. New devices and methods are thus needed for an ablation catheter having an ability to entrap and/or remove embolic debris generated during ablation of ectopic atrial foci in patients with atrial fibrillation or other sustained atrial arrhythmias, thereby reducing the risk of embolization.